1. Field of the Invention
The invention generally relates to imaging devices and particularly to integrated circuit imaging devices requiring compensation for process and other variations.
2. Description of Related Art
Integrated circuit imaging devices include an array of light detecting elements interconnected to generate analog signals representative of an image illuminating the device. One common example of an integrated circuit imaging device is a charge coupled device (CCD) which is relatively expensive and consumes a relatively large amount of power. An alternative integrated circuit imaging device employs complementary metal oxide semiconductor (CMOS) image sensing elements. Within such an integrated circuit, a CMOS photo-diode or photo-transistor is employed as a light detecting element.
In one example, conductivity of the element varies in accordance with the intensity of light illuminating the element. In another example, charge is collected in accordance with the intensity of light illuminating the element. By conducting current through the element or storing charge, an analog signal is generated having a magnitude approximately proportional to the intensity of light illuminating the element. CMOS integrated circuit imaging devices are considerably cheaper than CCD-type devices and may consume less power.
By having an array of these sensors, and image can be formed by reading the light intensity measured by the sensors, and reconstructing the image on a display device. The captured image can also be output to a printer or other output device.
In security applications, images often need to be authenticated in terms of the source of the images and the validity of the image (i.e., the image being identifiable from a particular sensor and not being edited from the original capture). Thus, order to ensure an image""s authenticity, the identity of source of the image must be unequivocally determinable. In addition, this allows an image, even if it has been modified, to be traceable to an original source.
Typically, such systems include, in addition to the integrated circuit imaging array, a separate controller circuit and a separate image processing logic circuit. The controller circuit controls the storage of the security/identification values and the application of those values for security/identification purposes. The controller may also provide timing signals for the proper clocking of the imaging array. The image processing logic may include, for example, logic for filtering the image or otherwise manipulating the image to perform pattern recognition and the like.
Thus, typical integrated circuit imaging devices often include separate integrated circuits for the imaging array, the controller and the image processing logic. The provision of separate integrated circuits for the various components, and corresponding separate packaging elements, results in a fairly high cost for the overall system. Each integrated circuit has to be tested individually, and also tested after they are mounted on a circuit board. If the assembled circuit board is determined to be defective, then the entire circuit board must be repaired or replaced.
Sensors are not identifiable when they are being manufactured. The security/identification values are assigned after the complete system is manufactured, resulting in an additional step in manufacturing that also adds to the cost of manufacture. There is also an administrative burden on keeping track of defective pixel information before an identification number is assigned as the sensor and the defective pixel information related to the pixel must be physically tracked throughout the manufacturing process. If a sensor is somehow misplaced in the manufacturing sequence, then the integrated circuit imaging array, and all the other integrated circuit imaging array that are mis-sequenced, have to be re-tested.
Moreover, the separation of the controller from the integrated circuit imaging array allows tampering of the security/identification values assigned to the imaging array. For example, a miscreant can replace the controller, and therefore, the security/identification values, associated with the array, thereby defeating the integrity of the system.
Currently, a certain number of defective pixels per sensor is tolerated so that a given amount of sensors are deemed usable and manufacturing costs are recovered. In these sensors, pixels that are found to be defective do not exceed a predetermined number for the entire sensor nor do they exceed a predetermined number within a predetermined area. Although the locations of these pixels are discovered during testing, it is an administrative burden, as described above, to keep track of this information during manufacture. More importantly, ensuring that information about defective pixels are supplied with each sensor after manufacture adds to the cost of sensor production. For example, the company that manufactures the sensor must provide the company that manufactures the camera with defective pixel information. Most often, the defective pixel information is provided a separate media (e.g., a floppy disc, a computer-readable tape, or other computer-readable storage media), which adds to costs. And again, problems arise with matching each sensor with its defective pixel information.
It would be desirable to provide an improved integrated circuit imaging system which overcomes these disadvantages.
A single integrated circuit having an image sensor for outputting signals representative of input light; a programmable non-volatile memory for storing defective pixel location information; a controller unit for interfacing with the programmable non-volatile memory and accessing the defective pixel location information; and a input/output port for communicating with control and post-processing circuitry.